The fact of composing polychromatic figures changing the color of lines, blots and drawings on paper, cardboard, etc. by chemical means is known and widespread as from the end of the 80's. In general, it deals with the application of inks formulated with coloring substances the structure of which includes reducible groups or bonds, whose reduction "in situ" with a suitable reducing agent causes the turning of the color of those portions touched or contacted by the reducing agent, when passing from the oxidized form to the reduced form. Of course, these are inks formulated with coloring substances the reduced form of which is not a leukobase: i.e., when the reduced form is clearly colored and specially makes contrast with the color of the oxidized form.
The idea of composing polychromatic figures by chemically acting on figures, blots, etc. of different colors has been commercialized under various generic names such as "magic inks" as, for example, the product called "Magicolor"
(Registered Trademark) developed by Sylvapen Distrib. S.A.C.I.F and other similar products based on the same principle.
In practice, these kinds of products are sold in assemblies or sets formed by writing and/or drawing fiber units or instruments, which are, per se, well known. Such sets include a plurality of instruments, one for each reducible color and another unit carrying the reducing agent and commonly called "eraser"--magic line (or stroke)--in the mentioned Magicolor product. In general, the eraser includes a sodium sulphite solution as reducing agent; although other reducing agents have also been proposed and tested, such as sodium thiosulphite, hydrosulphite and bisulphite, as well as the corresponding potassium salts, and even some organic reducing agents, such as formaldehyde or hydroquinone.
Therefore, products designated "magic inks", also known as "turnable inks", include an assembly of inks sensitive to a reducing agent (called "reducible ink" henceforward), carried by in writing and/or drawing instruments, while the reducing agent is contained in, and dispensed from, another similar instrument, whose lines or strokes are uncolored. I.e., the path of the instrument bearing the writing agent on paper, for example, is only distinguished at the regions covered by reducible inks, revealed by the appearance of the colors corresponding to the reduced forms of said inks.
Therefore, the color combination afforded by conventional "magic inks" or multiple color inks is limited by the number of reducible inks; i.e. by the number of writing and/or drawing instruments (henceforward also called "color units"). In fact, each color unit gives two different colors: one corresponding to the unreduced form and the other to the reduced form of each ink. In this way, the color spectrum which may be obtained with conventional multiple color inks only comprises colors of each ink and colors of the reduced form thereof, without any chromatic addition from the instrument carrying the reducing agent (from now on also called "reducing unit").